Whats with S&W 300 Chamber?

[crossgun]

Any info on the S&W 300 Whisper/Blackout chambers? Damn, they appear to be HUGE!

Wanted to test gas port size and function so ran to the range a fired a few rounds. Upon inspecting the once fired brass I couldnt believe how much the case necks and shoulders expanded. After firing they are like straight walled cases. They are way beyond SAAMI spec for the Blackout. I am aware that there is a slight difference in spec between the Whisper and Blackout but thought is was a free bore issue more than anything.

SAMMI spec on the chamber for the neck is .337 and the fired S&W cases measure like .350-.351! Doesnt appear to even be a shoulder in the chamber or hardly one.

Didnt get a chance to check for accuracy and now wondering? I did take a look with a bore scope and looks OK. Also compared it to another S&W and appears to be the same and not some freak accident.

Any info or thoughts?

Picured from L-R are two fired case from the S&W, one loaded round and lastly a fired case out of a Noveske barrel. The Noveske fired case and chamber even appear to be better or tighter than SAMMI as the fired case is still under sized according to the print.

http://i714.photobucket.com/albums/ww150/copperfield8910/DSCF1789.jpg
http://i714.photobucket.com/albums/ww150/copperfield8910/DSCF1787.jpg
http://i714.photobucket.com/albums/ww150/copperfield8910/DSCF1793.jpg
http://i714.photobucket.com/albums/ww150/copperfield8910/DSCF1792.jpg

[Robb Jensen]

Weird... I'd recommend calling S&W.

[Todd.K]

Our 300 BLK chamber is not tighter than SAAMI.

The case will shrink some after firing, so it can come out a bit smaller than the chamber.

[GunnutAF]

I think what your seeing is that the 300 Wisper- not a SAAMI spec'd chamber. Where as the 300 Blk is spec'd. Looks like that chamber was reamed alittle off spec. Thats going to shorten your brass life alot.:rolleyes:

[Makintrax73]

Might want to measure the cases for stretch also. With the small shoulder on a 300BLK, and the neck that loose, I wonder whether this might also create the possibility of a headspace issue.

The measurement just to the rear of the shoulder on an unfired round has to be slightly smaller than the .363" chamber spec in order to chamber. If your chamber's neck is slightly larger than .350" (to account for spring back) then you have not much material to headspace off, and the possibility that it won't stop the cartridge from chambering too deep. Based on that I would be afraid to shoot it.

Either way it can't be good to have the chamber neck .012" out of spec. A call to S&W is definitely in order.

[rsilvers]

http://www.300blktalk.com/forum/viewtopic.php?f=136&t=79606&p=746067#p746067